This invention relates generally to a propellant ignition system for use in a gas generator and, more particularly, to an ignitor for use in a gas generator utilizing a liquid monopropellant as a combined oxidizer/fuel source.
Over the past several decades there has been strong interest in liquid propellant technology, generally for use in propelling munitions. For example, U.S. Pat. No. 4,745,841, entitled "Liquid Propellant Gun", to Magoon et al, teaches a propellant gun wherein the mass rate of flow of a hydroxyl ammonium nitrate based liquid monopropellant can be repetitively, selectively and continuously varied throughout the interval of time of firing a single shot. This patent and all references cited therein are hereby incorporated herein in their entirety by reference. There are a number of energetic liquids which could be used for propelling munitions. For example, hydrazine and hydrogen peroxide are readily available. Hydrazine, however, is extremely toxic and requires stringent safeguards for human safety, while hydrogen peroxide, in concentrations of practical interest, is inherently unstable and is a severe fire hazard.
Liquid propellants are useful because copious amounts of gas are generated as the propellants burn, expand, and propel the munitions out from the gun barrel. Although large amounts of gas are produced, the reaction is an extremely short lived phenomenon, i.e., on the order of 10-20 milliseconds, and therefore liquid propellants have been heretofore limited in their applications. However, some applications need a substantial volume of gas delivered at a specified pressure over a given length of time, such as for the starting of rotating machinery (e.g., diesel engines and gas turbines), inflation of gas bags (e.g., deep sea salvage inflation devices and automotive air bags), and steady-state operation of turbine-driven machinery.
Filed concurrently herewith is U.S. patent application Ser. No. 08/452,901, entitled "Liquid Monopropellant Gas Generator", to K. Schaefer et al., which discloses and claims a liquid propellant gas generation system. This system includes a propellant storage tank, a motor-driven pump (or other pressurization means) to force the propellant into a combustion chamber, an injector to effectively break up the incoming liquid propellant into droplets that facilitate ignition and sustain combustion, an ignitor to initiate the combustion process, a nozzle to isentropically expand the exhaust gases in order to optimize the pressure and temperature of the exhaust gases, and exhaust ducting to direct the flow and handle further heat transfer requirements. The output of the gas generator may be varied either by throttling the exhaust gases or by setting up a plurality of continuous generators in a manifold assembly. This patent application and all references contained therein is hereby incorporated herein by reference.
One of the key elements of a liquid monopropellant gas generator is ensuring that the ignitor, which must ignite or initiate combustion of the propellant, creates an environment (pressure and/or temperature) within a combustion chamber of a gas generator to ensure combustion of the in-flowing propellant. Therefore, it is desirable to provide a simple and reliable ignitor to initiate combustion within a gas generator, particularly for igniting a liquid monopropellant, and for ensuring a proper environment for combustion in a liquid monopropellant gas generator.